The present invention relates to an assembled camshaft for an internal combustion engine, having an outer hollow camshaft body and an inner camshaft body disposed within the outer hollow camshaft body and mounted so as to rotate relative to it by a predetermined angle. In this connection, the camshaft has at least two different cam elements that can also be rotated relative to one another, at least in parts, by way of the camshaft bodies that can be rotated relative to one another.
During operation of internal combustion engines, it is desirable to be able to variably configure the opening and closing of the inlet and outlet gas exchange valves. In this manner, corresponding control of the gas exchange valves can be controlled in targeted manner, as a function of the operating state of the internal combustion engine, in order to achieve optimal behavior of the gas exchange valves.
A reciprocating internal combustion engine is disclosed in German patent document DE 42 40 631 A1, having at least two gas exchange valves per cylinder, where the cam elements that belong to or are assigned to the gas exchange valves, in each instance, are situated on camshafts that are disposed concentric to one another. By means of the concentrically disposed camshafts and the different cam elements, which are connected with different camshafts so as to rotate with them, accordingly, corresponding control of the cam elements relative to one another and a corresponding behavior of the internal combustion engine can be achieved by rotation of the camshafts relative to one another. In addition to this relative rotation of individual cam elements relative to one another, rotation of the entire camshaft—in other words of the two camshaft bodies disposed concentric to one another, together, in relation to the angle position of the crankshaft—is possible. In this way, further optimization of the gas exchange valve control with regard to the desired fuel reduction and/or power increase of the internal combustion engine can be achieved. A disadvantage of such an arrangement is the relatively complicated mechanical design for adjusting the inner camshaft relative to the outer camshaft, or for adjusting the overall camshaft in relation to the crankshaft. Further disadvantages of such designs are the required greater construction space as well as the costs, which are comparatively higher.
Furthermore, a camshaft having so-called expanding cams is known from European patent document EP 1 500 797 A1, in which shaft at least two partial cams of a cam element that can be rotated relative to one another is achieved by rotation of an inner camshaft body situated concentrically in the interior of an outer camshaft body, relative to the outer camshaft body. By means of the proposed configuration of cam elements as so-called expansion cams, the opening period of the valves, i.e. the time point of opening and/or closing of the gas exchange valves, as well as the duration of the valve overlap can be influenced at a constant stroke. If a long valve opening period is desired, the partial cams are brought into a position, relative to one another, in which the profile regions with constant stroke lie next to one another, seen in the axial direction of the camshaft (cam element expanded by means of rotation of the partial cams). In this way, the effect of a broad or steeper cam, i.e. one expanded in the circumference direction, can be achieved. Broadening of the cam element can furthermore lead to a greater overlap of the inlet and outlet valve. If, in contrast, a shorter opening period is desired, the partial cams are brought into a position, relative to one another, in which the profile regions with constant stroke are disposed essentially one behind the other, seen in the axial direction of the camshaft (cam element not expanded). In this way, the effect of a narrower cam/cam element, i.e. one strictly limited in the circumference direction, can be achieved.
An increase in the variability of the valve control is only possible by means of the additional adjustment of the entire camshaft relative to the crankshaft, using a second camshaft adjuster. This increases the costs, on the one hand, and worsens the installation situation with regard to utilization of the available construction space, on the other hand.
The present invention provides an assembled camshaft by means of which the most variable possible control of the gas exchange vales of an internal combustion engine is made possible, on the one hand, and in which the least possible effort with regard to adjustment of the cam elements relative to one another is implemented, on the other hand. The production costs are advantageously reduced, in comparison with conventional systems, by means of the simplest possible design structure, and the required construction space is supposed to be minimized.
According to the invention, this is accomplished in that the assembled camshaft comprises at least two separate cam elements, where a first cam element is connected with the inner camshaft body, in its totality, so as to rotate with it, and is disposed so as to rotate relative to the outer camshaft body, which is configured as a hollow camshaft body, and that a second cam element has at least two partial cam elements that can be rotated relative to one another, in such a manner that a first partial cam element is disposed on the outer hollow camshaft body, so as to rotate with it, and a second partial cam element is connected with the inner camshaft body, so as to rotate with it, and is disposed so that it can be rotated relative to the outer hollow camshaft body.
In a particularly preferred embodiment of the invention, the at least two different cam elements are disposed on the camshaft, axially spaced apart from one another, in such a manner that inlet-side or outlet-side control of at least a first gas exchange valve of a cylinder combustion chamber of the internal combustion engine is made possible by the at least one first cam element, and inlet-side or outlet-side control of at least a second gas exchange valve of the same cylinder combustion chamber is made possible by means of the at least one second cam element (in analogy to the first cam element). Thus, two inlet-side or two outlet-side gas exchange valves of a common cylinder combustion chamber are advantageously always activated by means of two different cam elements of the first and second construction type (and connection to the camshaft), disposed axially adjacent on the same camshaft (first cam element and second cam element), or stand in interaction with them, respectively.
In other embodiments, the at least one first cam element is assigned to the at least one gas exchange valve of a first cylinder combustion chamber, and the at least one second cam element is assigned to the at least one gas exchange valve of another cylinder combustion chamber.
In each case, the corresponding assignment is possible both on the inlet side and on the outlet side. Of course, the configuration of the camshaft according to the invention, which is implemented by means of the configuration of the different first and second cam elements or their placement on the hollow camshaft body or the inner camshaft body, can be expanded to include additional cam elements such as, for example, at least one cam element of a third type (also referred to as a third cam element). For example, the third cam element can be disposed, in its totality, on the outer hollow camshaft body, so as to rotate with it.
For relative rotation of the two camshaft bodies with regard to one another, a drive device is provided, which, in a first embodiment, acts on the outer hollow camshaft body and/or the inner camshaft body rotationally, or which, in another embodiment, acts on the inner camshaft body, particularly translationally, and thereby brings about a corresponding relative rotation with regard to the outer hollow camshaft body. Finally, a second drive device can be provided, for rotation of the entire camshaft relative to the position of the crankshaft of the internal combustion engine.
In another preferred further development of the invention, the at least one cam element of the second type (cam element having at least two partial cam elements that can be rotated relative to one another) is configured in such a manner that the two partial cam elements have a different maximal stroke height and the cam peak section of the partial cam having the lesser maximal stroke height has a cam contour section having a maximal stroke height formed by an arc section. With regard to the function and design configuration of the cam element configured in multiple parts, at this point the disclosure content of the German patent application having the official file number 10 2009 041 426.6, which is not a prior publication, is explicitly incorporated into the disclosure content of the present application. Alternatively or additionally, a cam element of the third type can also be structured by means of a cam element configured in multiple parts, according to German patent document DE 10 2009 041 426.6, or be present, respectively.
The invention furthermore relates to an internal combustion engine having such an assembled camshaft, where with regard to at least one cylinder of the internal combustion engine, at least a first cam element and a second cam element interact with a gas exchange valve of one and the same cylinder combustion chamber, on the inlet or outlet side.
Further characteristics, properties, and advantages of the present invention are evident from the following figure description of a preferred exemplary embodiment of the invention, making reference to the attached drawing figures.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.